A principal objective of coal benefication is to increase the calorific heating value or amount of thermal energy of the coal that can be released during a subsequent combustion process. One method of increasing the thermal energy released during combustion of coal is to decrease the amount of moisture by subjecting the coal to a drying process. It will be appreciated that moisture in coal has no heating value and, although not environmentally harmful, facilitates depletion because evaporation of the moisture consumes a portion of thermal energy released during combustion of coal.
Another known method of increasing the thermal energy released during combustion of coal is to decrease the amount of volatile matter within the coal, and thereby increase the relative amount of fixed carbon in the coal. The amount of volatile matter within coal may be decreased by subjecting the coal to a pyrolysis process. Pyrolysis of coal in an oxygen deficient atmosphere removes volatile matter, e.g. low boiling point organic compounds and some heavier organic compounds, by breaking chemical bonds during the heating process. Breaking chemical bonds within coal during the heating process increases the relative percentage of elemental carbon that provides most of the calorific heating value when the coal is burned.
Various aspects of conventional coal upgrading processes require a supply of fuel for providing the heat necessary to operate the process. In regions lacking a readily available supply of natural gas, the fuel must be shipped to the coal processing site, or alternate fuels must be used. Each of these substitute fuels can present problems in operating an efficient coal upgrading process.
When raw coal is subjected to a pyrolysis process, the resulting stream of volatiles is often subjected to a condensation process to remove tars and oils as a valuable byproduct of the coal treating process. In some cases the volatiles stripped from the coal in the pyrolysis process are used as fuel in the overall coal treating process. In many cases the volatiles stripped from the coal are a lean fuel, and have varying properties over time, i.e., an inconsistent chemical composition and calorific heating value over time. It would be helpful if there could be developed an improved coal upgrading process where the lean fuel volatiles from a pyrolysis step can be efficiently and reliably used as fuel source in the overall coal processing operation.